Supplementary data for the paper 'eHMI on the vehicle or on the infrastructure? A driving simulator study'

Automated vehicles (AVs) may require the implementation of an external human-machine interface (eHMI) to communicate their intentions to human-driven vehicles. The optimal placement of the eHMI, either on the AV itself or as part of the road infrastructure, remains undetermined. The current driving simulator study investigated the effect of eHMI positioning on human driving behavior, during the approach and execution of right turns at T-intersections. Forty-three participants drove under three conditions: absence of eHMI, eHMI on the AV (eHMIv), and eHMI integrated into the infrastructure (eHMIi). Participants encountered AVs that either yielded or did not yield to their vehicles. The results regarding the placement of the eHMI showed that both concepts are advantageous, but for different reasons. eHMIv was appreciated because implicit and explicit communication are congruent, although the AV must first be visually identified to respond to it. eHMIi was appreciated because a familiar cue is always at a known location in the environment; as a result, participants braked earlier for the intersection and came less close to the AV (which can be interpreted as a safety advantage or efficiency disadvantage). Although there are limitations to the current driving simulator study, this research provides important insights into the fundamental question of how information placement affects drivers’ visual attention demands and driving behavior, topics that are important in view of the development of future cities.

自动驾驶汽车（Automated Vehicles，AVs）通常需要搭载外部人机交互界面（external human-machine interface，eHMI），以向人类驾驶车辆传递自身行驶意图。此类外部人机交互界面的最优安装位置——要么设于自动驾驶汽车本体，要么集成于道路基础设施——目前尚未确定。本项驾驶模拟器研究探讨了在T型路口右转的接近与执行阶段，外部人机交互界面安装位置对人类驾驶员驾驶行为的影响。43名参与者在三种实验条件下完成驾驶任务：无外部人机交互界面、设于自动驾驶汽车上的外部人机交互界面（eHMIv），以及集成于道路基础设施的外部人机交互界面（eHMIi）。参与者会遇到两种情形的自动驾驶汽车：其一为礼让己方车辆，其二为不礼让己方车辆。针对外部人机交互界面安装位置的研究结果显示，两种安装方案均具备优势，但背后的动因各不相同。eHMIv获得参与者认可的原因在于，其隐式与显式信息传递完全一致，但该方案需先通过视觉识别到自动驾驶汽车，才能对界面信号做出响应。eHMIi获得参与者认可的原因在于，其提示信号位于驾驶员熟悉的环境固定位置；因此，参与者会更早对路口实施制动，且与自动驾驶汽车的车距预留更大——这一结果可解读为安全层面的优势，但同时也可能带来通行效率层面的劣势。尽管本项驾驶模拟器研究存在一定局限性，但该研究为「信息安装位置如何影响驾驶员视觉注意力需求与驾驶行为」这一核心问题提供了重要见解；而鉴于未来城市的发展规划，此类研究议题具备重要价值。